Developing Insights into Pretreatment Optimization: Effects of Eliminating Lime and Soda Ash in Groundwater RO Desalination

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript investigated the operational, economic, and environmental impacts of replacing lime–soda ash softening with an antiscalant-based pretreatment in a full-scale brackish groundwater reverse osmosis desalination plant in Saudi Arabia. The study provided a thorough comparative analysis covering water quality evolution, membrane performance, and cost efficiency. Its strengths lay in comprehensive field data, clear economic evaluation, and practical implications for sustainable desalination in arid regions. However, the work had several limitations, including limited statistical treatment of temporal variability, insufficient discussion on antiscalant composition and dosing optimization, and a lack of quantitative environmental impact assessment for brine management. The absence of long-term membrane integrity data also weakened the operational conclusions. Despite its novelty and strong practical orientation, methodological depth and broader generalization should be improved before publication. Therefore, I suggest the manuscript has to be reviewed after a Major Revision. The specific comments are as follows:

 

Major Concerns:

• Lines 26–28. The economic comparison lacked a detailed breakdown of cost sensitivity and uncertainty analysis, which limited the robustness of the claimed 54% reduction in operating expenditure.
• Section 2 Methodology. The study design did not sufficiently justify the selection of sampling frequency and duration to represent long-term operational stability.
• Lines 178–181. The water sampling approach covered only four process points and five replicates, which was insufficient for capturing seasonal or operational fluctuations.
• Lines 203–208. The description of scaling index calculation did not specify assumptions or boundary conditions in the Visual MINTEQ simulation.
• Lines 395–416. The discussion on feed pressure increase lacked quantitative correlation with specific fouling mechanisms or deposition rates observed on membranes.
• Lines 440–445. The line style in Figure 2 should not have been presented as a fitted smooth curve but as actual segmented lines connecting the measured data points.
• Lines 486–495. The economic evaluation excluded capital costs and membrane lifespan implications, which weakened the overall cost–benefit interpretation.
• Lines 552–559. The environmental assessment mentioned ecological risks qualitatively without quantifying reject stream composition or toxicity effects.
• Lines 569–582. The recommendations section restated results instead of providing actionable guidance for optimization or policy application.
• Lines 590–603. The conclusions provided only broad and general recommendations without offering deeper analytical insight or theoretical advancement, which limited the overall academic contribution of the study.
• Lines 600–607. The discussion of maintenance cost increase did not include predictive modeling or cost recovery assessment for different cleaning frequencies.

 

Minor Comments:

Minor grammatical errors should be corrected.

• Lines 19. The phrase “before the RO” should have been “before RO treatment” to maintain technical consistency.
• Lines 70–73. The sentence contained redundant modifiers (“particularly concerning due to their neurotoxicity”) and lacked proper comma placement.
• Lines 146–147. The phrase “designed to produce potable water through a combination of conventional and advanced treatment technologies” used unnecessary repetition.
• Lines 231–232. The sentence beginning with “An economic assessment was conducted” was excessively long and lacked a clear main verb focus.
• Lines 606–610. Several compound sentences used inconsistent tense and coordination, creating grammatical ambiguity.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript presents the insights into pretreatment optimization on the eliminating the lime and soda ash in groundwater RO desalination. This is an interesting subject in the RO desalination. However, several areas require improvement to strengthen the quality of the manuscript.

1. The English language of the whole manuscript should be professionally and carefully edited.
2. Abstract – The abstract is lengthy. The problem statement emphasizing on using lime-soda ash softening in RO should be addressed. Compared with the previous studies, what is the novelty of this study? Check the spelling, it is ‘old plan, new plan’ or ‘old plant, new plant’? Also specified the location/region/country of the groundwater studied in this study. Suggest to rewrite the abstract into problem statement, objective, methodology, significant findings and conclusions.
3. Introduction – Why RO is better compared to other processes like aeration, sedimentation, filtration? Since this paper presented an applied research study, suggesting the literature review should be focused more on the effects of operational parameters on the low chemical pretreatment strategies. The problem statement and novelty of this study are not clear.
4. Line 152 – Suggest to specify the salinity of the brackish groundwater as well.
5. Section 2.2 – Specify the volume of sample collected and the method to preserve the original water quality before the analysis.
6. The model/brand should be included for all the instruments. What type of RO membrane used in this study? Prefer to add more schematic diagrams to show more insights of this study.
7. Economic assessment – Should also include the equations and assumptions. What is the plant capacity considered in the economic analysis? Water recovery by the RO?
8. Tables 1-3: Show no significant improvement of using new plant as the concentrations of most parameters tested are low in old plant. This shows no promising result of this study. What is the purpose of water softening? Higher hardness of water is better than lower hardness?
9. Author should compare the water production rate (permeate) between the oil and new plants.
10. Economic assessment result: References are required to support the findings.
11. Conclusions – It is lengthy. Should be written in more concise which highlighted the findings of this study.

Comments on the Quality of English Language

Require improvement. 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Comments on the paper titled “Developing Insights into Pretreatment Optimization: Effects of Eliminating Lime and Soda Ash in Groundwater RO Desalintion” and written by Yazeed Algurainy et al.: This study touches an interesting topic such as pre-treatment evaluation in a full-scale BWRO desalination plant. In general, the paper is well written and structured, however there are som aspect that must be improved. I recommend a major revision based on the following comments:

1. Page 3, line 112. Please, use the abbreviation RO, revise the entire manuscript.
2. Figure 1. The authors showed the flow diagram of the desalination plant, which highlights the extensive pre-treatment used, despite the fact that it is groundwater. The pre-treatment includes cooling + aeration, sedimentation, sand filtration, and antiscalant dosing. This pre-treatment generates sedimentation sludge and wash water from cleaning the sand filters, which must be discharged, with the consequent economic and environmental impacts. I recommend that the authors take a critical look at the pretreatment stage of this plant. For example, there are studies that have published results of full-scale BWRO desalination plants using well groundwater as feed water, where pretreatment consisted simply of a microfiltration stage and antiscalant dosing. The performance showed in these studies is quite acceptable.
3. Generally, in BWRO desalination plants, feed water conditions pretreatment in terms of colloidal fouling, measured through SDI, MFI, etc., and the maximum recovery that can be obtained in the plant. The latter point is affected by salts that are less soluble in aqueous solutions, such as calcium carbonate. Does the treatment shown in this study increase the maximum recovery of the desalination plant? Compare the results with other studies that have taken into account similar types of groundwater and have estimated the maximum recovery of these systems simply by using anti-scaling agents in addition to microfiltration.
4. In line with the previous points, it would be interesting for the authors to compare the economic impact of the pretreatment shown with other simpler pretreatments, such as the one mentioned above (microfiltration + antiscalant dosing). There are studies that have evaluated the cost of antiscalant dosing considering different inorganic compositions of groundwater. This would add value to this study.
5. Something strikes me as odd. Table 3 shows some parameters for permeate concentrations, with TDS values around 80 ppm. How is it possible that Table 4 shows TDS results around 1000 ppm for the final desalinated water? What is the reason for this increase in concentration?
6. Do the authors have data on colloidal fouling of the feed water? It seems to me that there are too many pretreatment stages considering that we are treating groundwater, which normally, with just one microfiltration stage, for example, 5 micrometers, can achieve an SDI of less than 3.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors had carefully addressed all previous comments with clear revisions and sufficient new explanations. Therefore, I recommend the manuscript be accepted for publication.

Author Response

Comment 1: The authors had carefully addressed all previous comments with clear revisions and sufficient new explanations. Therefore, I recommend the manuscript be accepted for publication.

Response 1: We thank the reviewer for the positive evaluation and recommendation for acceptance. We sincerely appreciate their time and effort in reviewing our manuscript.

Reviewer 2 Report

Comments and Suggestions for Authors

This is a revised manuscript, and the authors have made a major revision on the manuscript by answering all the comments raised. However, a minor revision is still required for the comment below:

 

1. Page 12, Line 481, should be Figure 2C; Line 486, should be Figure 2A-B.

 

Author Response

Comment 1: Page 12, Line 481, should be Figure 2C; Line 486, should be Figure 2A-B.

Response 1: We thank the reviewer for noticing this typographical error. The figure citations have been corrected in the revised manuscript as follows: Page 12, Line 481 now refers to Figure 2C, and Line 486 now refers to Figure 2A–B.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have adressed all my comments. There is only one aspect that should be reviewed: there are repeated references.

Author Response

Comment 1: The authors have adressed all my comments. There is only one aspect that should be reviewed: there are repeated references.

Response 1: We thank the reviewer for this helpful observation. The entire reference list has been carefully reviewed, and all entries were cross-checked for duplication by author names, titles, and publication years. We confirm that no repeated references are present in the revised manuscript.